Guide pads are used during cutting machining in metals and other hard materials on e.g. cutter heads of deep hole drilling tools in order to prevent wear of the cutter head and to guide the drilling tool during the drilling process and thereby maintain the cutter head on a straight axis line to create a bore hole which is straight with an as high accuracy as possible. For this purpose at least two guide pads are mounted in a respective seating on an outer periphery or envelope surface of the cutter head by means of e.g. screwing, clamping or soldering. A sliding surface of the guide pad which is facing outwards and bears against the circumferential hole wall of the bore hole, is normally formed with a part-circular cross section having the same or a somewhat smaller radius of curvature than the radius of the bore hole.
During the drilling process, the guide pad is exposed to high temperatures due to friction against the hole wall which, in combination with high pressure against the hole wall, makes the guide pads subjected to wear and formation of cracks. In order to reduce the tendency of wear and crack formation, it is common practice to provide a cooling and lubricating fluid, which is fed through channels within the drilling tool into the bore hole. However, the cooling/lubricating fluid can often not to a sufficient extent reach the entire contact zone between the guide pad and the hole wall, which makes the cooling/lubricating insufficient such that the wearing of and formation of cracks will still be considerable.
To overcome this problem it is known to provide guide pads with grooves or channels of different shapes and in different patterns in the sliding surfaces which are adapted to facilitate conveying of a cooling and lubricating fluid to the contact surface of the sliding surface which is in contact with and bears and slides against the hole wall during drilling.
Such guide pads are shown for example in DE 20 2009 003645 in which are disclosed guide pads being provided with one or more grooves in a direction in parallel to a longitudinal axis of each guide pad. A problem with such a design is that the grooves will function as indications of fracture or stress concentrations which will weaken the guide pad and necessitate increasing of its overall thickness.
Another example of a guide pad being formed with grooves is disclosed in WO 2012/172537 in which two grooves extend from a middle portion of the guide pad and diagonally towards the corners between the longitudinal side surfaces and the end surface at each end of the guide pad. Besides weakening the guide pad, these grooves will not to a sufficient extent provide the contact surface with a sufficient amount of cooling and lubricating fluid.
Also US 2013/0051944 discloses in FIG. 5 a guide pad being provided with grooves, which extend both in parallel to as well as perpendicular to the longitudinal axis of the guide pad. Of course, also these grooves will weaken the guide pad to a great extent. In FIG. 9 is disclosed an alternative embodiment, which is formed with closed, pocket-like lubricating grooves, which are adapted to function as reservoirs for lubricating fluid. These grooves will not weaken the guide pad to the same extent as the grooves described above. However, the closed design of the grooves will also prevent supply of sufficient amounts of lubricating fluid to the grooves.